The present invention relates to improvements in the field of electrocoagulation. More particularly, the invention is concerned with an improved method of reproducing an image by the electrocoagulation of an electrolytically coagulable colloid.
Applicant has already described in his U.S. Pat. No. 3,892,645 of July 1, 1975 an electrocoagulation printing method and system in which a thin layer of a liquid composition containing a colloid such as gelatin or albumin, water and an electrolyte is interposed between at least one pair of opposite negative and positive electrodes spaced from one another to define a gap which is filled by the liquid composition. In one embodiment, there is a plurality of electrically-insulated juxtaposed negative electrodes and selected ones thereof are electrically energized to pass electric pulses through the layer at selected points to cause point-by-point selective coagulation and adherence of the colloid in variable thickness on the positive electrode directly opposite each energized negative electrode, thereby forming dots of coagulated colloid representative of a desired image which may be transferred onto an end-use support, such as paper.
A major problem encountered with such an electrocoagulation printing method is that since the negative electrodes are generally energized more than once in the reproduction of an image, these become polarized resulting in secondary electrolytic reactions causing the generation of hydrogen bubbles which remain trapped at the interface of the negative electrodes and thus adversely affect the image reproduction. It has been observed that when forming the first series of dots of coagulated colloid there is no such undesirable gas generation and accumulation at the negative electrodes, but after the first electrocoagulation hydrogen generated by electrolysis slowly builds up and creates an electrical resistance at the interface of the negative electrodes such as to cause the formation of the dots of coagulated colloid to become erratic.